The use of diaphragm pumps to move or propel fluids, slurries, or the like, from one location to another, is well-known. The multiple diaphragms are customarily actuated by compressed air or hydraulic fluid, the diaphragms being connected by a common shaft, whereby the diaphragms move simultaneously in a parallel path. Diaphragm movement is conventionally powered by compressed air, as described in U.S. Pat. No. 3,338,171, or by hydraulic fluid, as described in U.S. Pat. Nos. 2,625,886, 3,652,187, 3,791,768 and 3,976,401. In accordance with the teachings of these patents, air or hydraulic fluid is directed against a side of a diaphragm of one chamber while air or hydraulic fluid is exhausted from behind the diaphragm of the other chamber. When the stroke is complete, an air or hydraulic valve automatically transfers the air or hydraulic fluid flow to the diaphragm of the second chamber, while the air or hydraulic fluid in the first chamber is exhausted. The continuous reciprocating motion of the shaft creats an alternate suction and discharge of the material in each chamber. Suction and discharge valves control the flow of material through the intake port of the pumping chambers and out the discharge port thereof.
With the prior art diaphragm pumps, where the pump is employed for spraying abrasive slurries which are conventionally employed for sealing asphalt surfaces, the spray pattern changes as the spray nozzles wear due to gradually enlarging the hole in the nozzles by the abrasive slurry, thereby producing a lower pressure drop and a smaller spray pattern.